It makes sense comparing Onkyo TX-SR373 vs Onkyo TX-RZ710 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Onkyo TX-SR373 has 5.1 versus 7.2 for Onkyo TX-RZ710. Regarding power, then TX-SR373 has such a W/Ohm ratio - 135/6 when TX-RZ710 has a power of 175/6. The THD is 0.06% for the TX-SR373 but 0.08% for the TX-RZ710.
Characteristics of digital to analog converter (DAC) are different, 192 KHz/24-bit for TX-SR373 and AK4458 384 KHz/32-bit for the TX-RZ710. Only the TX-RZ710 supports Bi-amping feature. The Onkyo TX-RZ710 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. Only the TX-RZ710 supports Spotify.
These units support HDR technology. Compared AV receivers retain the quality of 4K/60Hz signal when transmitting from a source to a TV or projector. HDMI signal transmission in standby mode is implemented in each of the devices. The TX-RZ710 can scale the input HDMI signal, unlike the TX-SR373. The HDR standard - Dolby Vision is not supported by these receivers.
The Onkyo TX-SR373 has 4/1 HDMI inputs/outputs versus 8/2 HDMI connectors of the Onkyo TX-RZ710. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. Both models support the standard HDCP 2.2. The TX-RZ710 has a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is only available for the TX-RZ710. Unfortunately, the setup assistant is not available in each of the models.
Only the TX-RZ710 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the TX-RZ710.